1. Field of the Invention
The present invention relates to a battery state monitoring circuit for monitoring a battery state, and to a battery device.
2. Description of the Related Art
A conventional battery state monitoring circuit and a conventional battery device are described. FIG. 5 illustrates the conventional battery state monitoring circuit and the conventional battery device.
A battery 21 is connected to a power supply terminal 16 and a ground terminal 17 of a battery state monitoring circuit 1. A charger 31 is connected to an external power supply terminal 26 and an external ground terminal 27. A load 32 is connected to the external power supply terminal 26 and the external ground terminal 27. A charge control transistor 22 and a discharge control transistor 25 are connected between the external ground terminal 27 and the battery 21. A charger detection terminal 20 is connected to the external ground terminal 27 via a resistor 2.
The battery state monitoring circuit 1 monitors a voltage of the battery 21. When the voltage of the battery 21 is higher than an overcharge voltage, an overcharge detection circuit 12 outputs a signal for turning OFF the charge control transistor 22 to a charge control terminal 18. When the voltage of the battery 21 is lower than an overdischarge voltage, an overdischarge detection circuit 14 outputs a signal for turning OFF the discharge control transistor 25 to a discharge control terminal 19.
When the charger 31 is connected to the external power supply terminal 26 and the external ground terminal 27, a voltage of the charger detection terminal 20 becomes a negative terminal voltage of the charger 31, and a voltage detection circuit 11 can thus detect the connection of the charger 31. When the charger 31 is not connected to the external power supply terminal 26 and the external ground terminal 27, the voltage of the charger detection terminal 20 is pulled up by the load 32 and the resistor 2 to a positive terminal voltage VDD of the battery 21. This way, the voltage detection circuit 11 detects that the charger 31 is not connected (see, for example, Japanese Patent Application Laid-open No. 2001-169463).
The battery state monitoring circuit 1 detects the connection of the charger 31 in such a way to perform various kinds of state control.
However, the conventional battery state monitoring circuit 1 requires the charger detection terminal 20 in order to detect the connection of the charger 31. The battery device of FIG. 5 exemplifies the case of the single battery 21. But, if a plurality of the batteries 21 are connected in series, the number of terminals connecting to the batteries increases corresponding to the number of batteries. Because the battery state monitoring circuit 1 is sealed in a package, if the number of terminals of the battery state monitoring circuit 1 exceeds the number of terminals of the package even by one, there arises a problem that the battery state monitoring circuit 1 can no longer be sealed in the package. In other words, even one terminal is desired to be eliminated.